Not 100% sure without looking at some reviews. But I would imagine the sigma was better. Sigma make good wide angle lenses. Tamron aren't really known for there wide angle lenses. Read some reviews online and you will probably find some detailed explanations on the image quality of both lenses.

James > Reviews arent any good here (i read on both) when we want to compare and choose the better one. Each review highlights each lens respectively on its pros and cons. But not in relativity to each other.

So when comparing like this, its more just comparing numbers and specs mathematically.

I agree you won't get a complete comparison but you can compare them. It will highlight if there are any problems with the lens and how stuff like how much distortion is apparent. It won't tell you the answer but will help. It will also show charts of sharpness at different apertures which you can compare between the lenses

Actually ive read the reviews in detail on both, including the test charts etc on lenstip.com and yet each has its pros n cons. Only members here can tell us in an unbiased manner as to how these lenses handle in the real world.

I just got the Sigma 10-20mm. Was shooting with it this whole afternoon. What i feel may sound absurd but i didnt find it visually epoch making wide when compred to the default 18-55mm kit lens. Sharpness and clarity also seems to be on par with an 18-55 kit lens.

But plz dont flame me for this hmmm, it may even be that ive not worked enough with the lens and hence lack the knowledge to shoot with it properly.

I didnt get around to uploading the pics to flickr but the lens i got is certainly extremely bad in quality. I cant believe a company like Sigma can have such bad QC issues.

It stands nowhere in sharpness to even my 18-55 kit lens. I felt real bad that i didnt see the amazon.com reviews that 50% of the units had soft focus issues. And blurry muddy images. I take a picture @ 10mm inside a small room objects 10 feet away are smudged.

Only when i saw these symptoms and googled with the symptom related workds did i find the amazon.com reviews where 50% of the people who bought the lens have received a bad copy. Even the other half of happy customers are ones who sent the lens back and got a proper copy replacement and only then did they give it 5 stars. In my country they never take it back. I have to suffer with a crap piece of glass that i spent $560 for just about 5 days back. Its a shame on Sigma. And my bad luck that none of the members here had this soft focus issue to warn me about.

I dont think ill EVER buy a sigma again.

If any of you know if i can email sigma's head office and ask them to do something about this that would be really helpful.

"Only when i saw these symptoms and googled with the symptom related workds did i find the amazon.com reviews where 50% of the people who bought the lens have received a bad copy"

If you google "Elvis is alive" you will even get more hits.

Any company that produced a product with a 50% defective ratio would be long gone.
As it was mentioned earlier, this is "specialty glass" and it takes time to understand how to use it. I'm sure that 100% of people that use a fisheye lens for the first time think its busted as well.